Methods of making electromagnetic devices



Sept. 11, 1962 R. HYlNK 3,052,959

METHODS 0F MAKING ELECTROMAGNETIC DEVICES Sept. 11, 1962 R. HYxNK 3,052,959

METHODS OF MAKING ELECTROMAGNETIC DEVICES Original Filed Dec. 2l, 1956 2 Sheets-Sheet 2 L1 .sa La United States Claims. (Cl. 29-15S.57)

This invention relates to methods of making electromagnetic devices.

While not limited thereto, the invention is especially applicable to productoon of alternating current contactors and relays operated at high ambient temperatures in control systems of aircraft and the like Where good quality of performance and low noise are required.

Irvin W. Cox application Serial No. 626,471, filed December 5, 1956, now Patent No. 2,925,540', dated February 16, 1960, and assigned to the assignee of the present application, discloses a cylindrical electromagnetic device constructed by winding a strip of magnetic material onto an arbor and milling across one end to produce four angularly spaced pole pieces. Preformed coils surrounding the pole pieces are energized from an alternating current supply source having a frequency in the range of approximately 180 to 1,000 cycles so that pairs of diametrically opposite coils have a phase displacement of approximately 9()y degrees. It has been found desirable to wind the strips of magnetic material for both the core and the armature on tubular internally flanged nonmagnetic arbors which can =be left in the finished products to provide internal support for the laminations. It is also desirable to construct both the core and armature without use of organic materials to bind the laminations to provide an electromagnetic device capable of withstanding extremely high temperatures'. It is further desirable to reduce the weight of the armature to the lowest possible value without decreasing the efficiency of the device.

'Accordingly it is the object of the present invention to provide improved methods of making an electromagnetic device embodying the aforementioned and other advantages.

Other objects and advantages of the invention will hereinafter appear.

While the methods hereinafter described are effectively adapted to fulfill the objects stated, it is to be understood that I do not intend to con-line my invention to the particular details of the method steps, inasmuch as they are susceptible of various modifications without departing from the scope of the appended claims. f

In the accompanying drawings:

FIGURE 1 is an end view of an electromagnetic device constructed in accordance with the present invention;

FIG. 2 is a side elevation view of the electromagnetic device of FIG. 1;

FIG. 3 is an end View of an armature constructed in accordance withthe present invention;

FIG. 4 is a cross-sectional view taken along lines 4-4 of FIG. 3;

FIG. 5 shows diagrammatically an electrical energizing circuit for the electromagnetic device of FIG. l; and

FIG. 6 is a vector diagram graphically depicting directive and quantitative characteristics of the electrical circuit of FIG. 5.

Referring to FIGS. 1 `and 2 there is shown a cylindrical electromagnet indicated generally as 1 comprising a cylindrical core 2 having integrally formed at one end thereof four angularly spaced pole pieces 3, 4, A5 and 6. Surrounding the respective pole pieces are four preformed operating coils 3a, 4a, 5a and 6a for introducing magl arent netic fields adjacent pole faces 7. Core 2 has an axial bore 8 which is lined with a sleeve 9 secured in the bore frictionally or by other appropriate means. Sleeve 9 has an internal iiange 1t) at one end for securing the magnet to a base (not shown) while the other end of sleeve 9 adjacent the pole faces '7 has a chamfer 11 to facilitate assembly of the preformed coils on the pole pieces. Sleeve 9 is formed of stainless steel or other non- .magnetic material having a greater resistance to wear than core 2. Thus, sleeve 9 at its chamfered end adjacent pole faces 7 is slightly shorter than core 2 so that a small amount of wear of the pole pieces Will not leave sleeve 9 extending beyond the surfaces of the latter to prevent sealing of an armature. The core laminations are welded together at the end away from the pole pieces as indicated at l2 to produce a unitary structure.

\ Electromagnet 1 is constructed by winding a ribbonlike strip of silicon steel or other magnetic material onto a preformed non-magnetic arbor similar to sleeve 9 4to produce a cylindrical core 2 having a plurality of thin laminations separated by an oxide layer or coating on the lamination stock material or by a suitable commercial insulating coating capable of withstanding high tem-V peratures without failure. The completely wound core assembly is held together by mechanical means such as a clamp or binding wire while it is annealed to remove stresses caused by bending the lamination material or otherwise during the winding operation. It is essential that the assembly be annealed at this time to relieve stresses which otherwise would become fixed during the ensuing welding operation. The core assembly is then welded in perpendicular directions across the end away from the pole pieces as indicated at 12 in FIG. 1 to fasten the laminations together in a unitary structure. The well known heliarc process is preferably employed wherein the welding is preformed in a medium of argon gas or the like and without addition of welding metal which might affect the magnetic characteristics of the core. Thus, a unitary core structure is produced within the device itself without introducing auxiliary fastening means into the flux path. Coil slots are produced by machining in perpendicular directions across one end of the core including sleeve 9 to a desirable depth axially of the core. The machining operation produces four pole pieces of substantially triangular cross-section each having a long outer convex surface and two straight converging surfaces ending in a short concave surface defined by a portion of the axial bore of the core. As shown in FIG. l, the welds 12 shown in broken lines are made along the rear end surface of the core at radial points bisecting the pole pieces which are on the front end sealing surface of the cylindrical core; that is, the welds are at radial points in the planes of the center lines of the pole pieces. As the magnetic flux between the opposed pole pieces of each pair thereof divides and one-half thereof is carried by each side of the core, it will be apparent that the welds are at points of minimum magnetic ux. Alternatively, the coil slots can be produced by punching to remove rectangular portions from one edge of the laminationV strip during the winding operation. The pole faces are ground to produce smooth surfaces for sealing with an armature hereinafter described. In the event the coil slots are produced by the aforementioned machining operation the core is annealed a second time to relieve internal stresses caused thereby, followed by final grinding to produce finished sealing surfaces. The two grinding operations hereinbefore described are required due to the heat evolved in removing a large amount of metal.

If only a small amount of metal need be removed to l.

produce smooth sealing surfaces, the irst mentioned grinding operation may be omitted. The assembly is then etched by applying a highly volatile acid such as U diluted hydrochloric acid or the like to remove grinding burrs which might shunt the laminations of the core, and thereafter baked to remove excess acid. Alternatively, such burrs can be removed by lapping which would obviate the necessity for the baking operation.

It should be noted that no organic materials are used to bind the core laminations so that the magnet can be used at extremely high temperatures without failure, limited solely by the maximum temperature that the coil including its insulation can withstand. Lamination stock material is provided with a thin insulating coating and dur-ing the usual manufacturing operations added insulation of the magnet laminations is obtained by applying a finely divided powder of magnesium oxide or the like before winding the core. It has been discovered that the use of such additional insulating powder may be omitted because inclusion thereof resulting in a reduction of energy losses would necessitate addition of resistance in the coil circuits to correspondingly increase the energy losses to maintain the Voltage at an acceptable Value as hereinafter described.

Referring to =FIGS. 3 and 4 there is shown a cylindrical armature for cooperation with the electromagnet of FIG. l. Armature 15 is comprised of spirally wound laminations of magnetic material such as silicon steel or the like and has a smooth surface 16 at one end for sealing with pole faces 7. The other end of armature 15 has a frusto-conical internal surface 19 obtained by cutting out a portion to afford a reduction in its weight without a corresponding decrease in eiciency. In electromagnets of the character hereinbefore described, the effective cross-sectional area of the armature need be no more than 70 percent of the cross-sectional area of its associated pole piece. The aforementioned relation accrues from the fact that localized parts of the armature carry one-half of the combined uxes of two of the pole pieces with approximately 90 degrees phase displacement therebetween.

Extending axially through the armature is a bore 17 lined with a sleeve 18 of non-magnetic material such as stainless steel or the like to provide support for the extremely thin laminations. Sleeve 118 has an internal flange 20 at the end immediately adjacent the conical surface 19 to facilitate attachment of the armature to a driven element such as a contact actuator or the like while the other end of sleeve 18 is internally chamfered at 21 and extends to an area slightly short of sealing surface 16 to prevent irregularity in such surface as a result of armature wear, sleeve 18 having a greater resistance to wear than the laminat-ions.

Armature 15 is constructed in the manner of electromagnet 1 by winding a ribbon-like strip of silicon steel or other magnetic material onto a preformed non-magnetic arbor similar to sleeve 18. In the manufacture of both the electromagnet and the armature the arbor is left in the nished product to provide supporting and securing means for the respective parts. Armature 15 is annealed, machined to form the conical surface 19, welded along the conical rear surface as indicated at 22 in FIG. 3 and ground to produce a smooth front sealing surface 16. The armature is annealed to relieve internal stresses caused by the aforementioned machining and welding operations followed by final grinding to produce a finished surface and application of diluted hydrochloric acid or the like to remove `any grinding burrs which otherwise might shunt the laminations of the armature. Thereafter the armature is baked to remove excess hydrochloric acid.

As described in connection with electromagnet 1, the number of grinding operations required depends upon the amount of metal that must be removed to produce a smooth sealing surface 16. 1f the winding operation leaves a surface requiring the removal of only a small amount of metal, grinding may be limited to the last mentioned final grinding operation. Likewise, removal of "5 grinding burrs by lapping in preference to etching would obviate the necessity for the final baking step.

The process hereinbefore described produces an armature which can be used without failure in ambient temperatures up to the Curie point of the steel of which it is formed. For best results armature 15 should be oriented relative to electromagnet 1 so that welds 12 and 22 are superimposed in the axial direction. With this orientation and because the magnetic flux between the opposed pole pieces divides and one-half thereof is carried by each side of the cylindrical armature, the welds 22 shown in FIG. 3 will be at radial points of minimum magnetic flux.

There is shown in FIG. 5 a circuit diagram for energizing the aforementioned operating coils 3a, 4a, 5a and 6a of the electromagnet in FIG. l. It may be assumed that supply lines L1 and L2 are connected to an alternating current supply source (not shown), such as 400 cycles used in aircraft systems, through suitable switches well known in the art. `Coils 3a and 4a which surround first oppositely disposed pole pieces 3 and 4, respectively, are connected in parallel across lines L1 and L2 to be energized in a given phase relative to the phase of the supply source. Coils 5a and 6a which surround second oppositely disposed pole pieces 5 and 6, respectively, are series connected with a phase shifting capacitor C across lines L1 and L2.

To obtain maximum quiet sealed pull in magnet 1 the flux in two diametrically opposite pole pieces must be equal to and displaced approximately degrees in phase relative to the flux in the other two diametrically opposite pole pieces. Such phase displacement is obtained by use of the aforementioned capacitor C in series connection with operating coils 5a and 6a.

In order to obtain the most efficient operation with a given core, the electrical values of the operating coils and capacitor are ascertained in a manner hereinafter described. Referring to the vector diagram in FIG. 6, first let it be assumed that the phase angle 0 of coils 3a and #la is ascertained. Since the phase of voltage ELC must be displaced approximately 90 degrees relative to the phase of voltage EL to obtain the hereinbefore described flux relations, voltage vectors BLG and EL can be drawn as shown. Thus, the position of current vector I1 is found because its phase angle is determined by the iron losses in the core and these losses have the same value for each identical pole piece. Voltage EC must be at a 90 degree phase relation to I1. Since Therefore, vfour identical coils can be used if they are connected as shown in FIG. 5. For a given value of flux in each pole piece, the same magnitude of current will flow in each coil. Therefore tan 0:2

21rfEc 41rfEL lf f=400; -tan 6:2; 0=63.5 degrees; and cos 0:.436

.4361', seno-m,

C- EL Let it be assumed that 12:.05 and EL=80 Then lf the magnitude of current I2 should increase slightly due to improper seal of armature 15 to the pole faces, it will be apparent from Equations 9 and 10 above that the size of capacitor C will have to be larger. A capacitor having a value of approximately .07 microfarad should be sufciently large to compensate for such line current variation and to maintain the desired phase relation.

The voltage `across capacitor C is EL divided by cos 0 or 2.24 EL. This Will give a maximum voltage Ec of 278 volts R.M.S. or 391 volts peak for a line voltage of 124 volts. As hereinbefore mentioned, applicant omits the use of additional insulation in the laminations of the core in order to maintain the voltage at this desired value. Thus, applicant can use a capacitor having Va standard voltage rating of 400 volts peak rather than a 600 volt capacitor With a corresponding increase in size and cost, and can omit the resistor previously employed in series connection with the capacitor for the purpose of maintaining the voltage at a desired value.

This application is a division of Roy Hyink copending application, Serial No. 629,984, filed December 21, 1956.

I claim:

1. A method of making an electromagnetic device suitable for relatively high frequency alternating current service, comprising the steps in the order stated of Winding a strip of magnetic material onto a non-magnetic arbor to provide a cylindrical laminated member, annealing said member to relieve internal stresses therein developed during winding, fusing portions of one end of said member radially at points of minimum flux which points are at the center line of each pole face to fasten said laminations together to provide a unitary structure, machining in perpendicular directions across the other end of said member to provide a plurality of angularly spaced pole pieces, grinding said other end of said member to provide sealing surfaces on said pole pieces, annealing said member to relieve stresses therein, grinding Said pole pieces to provide said sealing surfaces With a smooth finish, etching said member with a volatile acid C .056 microfarad to remove grinding burrs to prevent shunting said laminations, and baking said member to remove excess acid.

2. A method of making an electromagnetic device suitable for relatively high frequency alternating current service which comprises the steps in the order stated of Winding a strip of magnetic material on a nonmagnetic arbor to provide a substantially cylindrical laminated member having a front sealing surface at one end and a rear surface at the other end, annealing said member to relieve stresses developed therein during Winding, radially fusing the laminations together along said rear surface at said other end of said member along paths Where the flux concentrations in use of the member Will be at a minimum, grinding the opposite end of said member to provide a smooth sealing surface, and then subjecting the last mentioned end of the member to an etching solution to remove burrs and metal overlapping the lamination ends which result from grinding.

3. The method as deiined in claim 2, having the additional step intermediate the fusing and grinding steps of machining an end of said member to provide a predetermined shape.

4. The method as dened in claim 2, having the additional step intermediate the annealing and fusing step of reaming said rear end to remove a truste-conical portion of material therefrom to reduce its Weight Without decreasing its eiciency.

5. A method of making an electromagnetic device suitable for relatively high frequency alternating current service which comprises the steps in the order stated of winding a strip of magnetic material on a non-magnetic arbor to provide a substantially cylindrical laminated member, annealing said member to relieve stresses developed therein during Winding, radially fusing the laminations together on one end of said member along paths Where the llux concentrations in use of the member will be at a minimum, machining an end of said member t0 provide a predetermined shape, grinding the opposite end of said member to provide a smooth sealing surface, and then subjecting the last mentioned end of the member to an etching solution to remove burrs and metal overlapping the lamination ends which result from grinding, said machining step comprising machining said opposite end of the member to provide a plurality of angularly spaced pole pieces so positioned that any radial fusion path on said one end angularly bisects a pole piece.

References Cited in the le of this patent UNITED STATES PATENTS 1,585,566 Sindl May 18, 1926 1,619,399 Brace Mar. 1, 1927 2,293,951 Seastone et al. Aug. 25, 1942 2,305,650 Vienneau Dec. 22, 1942 2,356,972 Chubbuck Aug. 29, 1944 2,376,613 Nelson May 22, 1945 2,394,047 Elsey et al. Feb. 5, 1946 2,469,808 Aske May 10, 1949 2,478,030 Vienneau Aug. 2, 1949 2,557,249 Aske `Tune 19, 1951 2,851,129 Doerries Sept. 9, 1958 

